Do you keep a rooster? That looks like damage from the rooster. If so, the proper ratio of rooster to hen is 1 to 10. If there is not enough hens for the rooster to mate, they can over mate, damage and injure the hens. So separate the rooster from this hen so she heals. In the future when this hen is healed, you can get her a hen saddle to protect her back....http://www.hensaver.com